Silicon carbide crystals and silicon carbide wafer

[0001] This application claims the priority benefits of U.S. provisional application Ser. No. 63/359,203, filed on Jul. 8, 2022, U.S. provisional application Ser. No. 63/359,205, filed on Jul. 8, 2022, and U.S. provisional application Ser. No. 63/359,208, filed on Jul. 8, 2022. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification.

[0002] The present disclosure relates to silicon carbide crystals and silicon carbide wafer.

[0003] At present, silicon wafers have been widely used in the semiconductor industry. Many electronic devices contain silicon wafers produced using silicon wafers as materials. However, in order to improve wafer performance, many manufacturers have attempted to use silicon carbide wafers as materials for producing silicon carbide chips. Silicon carbide wafers have the advantages of high temperature resistance and high stability.

[0004] As far as the prior art is concerned, when growing N-type silicon carbide crystals, a common method is to increase a nitrogen doping concentration, so that the resistivity can be lowered, which will be better for downstream components, and the electrical performance will also be improved. However, high doping concentration is likely to cause an increase in basal plane dislocations (BPD) and bar stacking faults (BSF), the industry generally avoids the use of high doping during crystal growth, which in turn results in a high resistivity and poor uniformity of the resistivity. If the silicon carbide crystal has a uniform resistance distribution, the crystal stress can be reduced, and the geometry of the processed wafer will also be improved. In addition, the electrical properties and performance of a silicon carbide device fabricated therefrom will also be improved. Based on the above, how to produce silicon carbide crystals and wafers with uniform resistivity is a problem to be solved.

[0005] The present disclosure provides a silicon carbide crystal and a silicon carbide wafer, and by controlling a ratio difference between an axial temperature gradient and a radial temperature gradient of the silicon carbide crystal and adjusting the doping amount of the nitrogen concentration, the formed silicon carbide crystal and silicon carbide wafer will have uniform resistivity.

[0006] The present disclosure provides a silicon carbide crystal, wherein a monocrystalline proportion of the silicon carbide crystal is 100%, a resistivity of the silicon carbide crystal is in a range of 15 mΩ·cm to 20 mΩ·cm, and a deviation of an uniformity of the resistivity of the silicon carbide crystal is less than 0.4%.

[0007] In one embodiment of the present disclosure, the monocrystalline proportion of the silicon carbide crystal is 100%, a resistivity of the silicon carbide crystal is in a range of 19 mΩ·cm to 20 mΩ·cm, and a deviation of an uniformity of the resistivity of the silicon carbide crystal is less than 0.4%.

[0008] In one embodiment of the present disclosure, the deviation of the uniformity of the resistivity is less than 0.01%.

[0009] In one embodiment of the present disclosure, basal plane dislocations (BPD) of the silicon carbide crystal is less than 200/cm².

[0010] In one embodiment of the present disclosure, basal plane dislocations (BPD) of the silicon carbide crystal is less than 140/cm².

[0011] In one embodiment of the present disclosure, a bar stacking fault (BSF) of the silicon carbide crystal is less than 5/wafer.

[0012] The present disclosure provides a silicon carbide wafer, wherein a monocrystalline proportion of the silicon carbide wafer is 100%, a resistivity of the silicon carbide wafer is in a range of 15 mΩ·cm to 20 mΩ·cm, and a deviation of an uniformity of the resistivity of the silicon carbide wafer is less than 0.4%.

[0013] In one embodiment of the present disclosure, the monocrystalline proportion of the silicon carbide wafer is 100%, a resistivity of the silicon carbide wafer is in a range of 19 mΩ·cm to 20 mΩ·cm, and a deviation of an uniformity of the resistivity of the silicon carbide wafer is less than 0.4%.

[0014] In one embodiment of the present disclosure, the deviation of the uniformity of the resistivity is less than 0.01%.

[0015] In one embodiment of the present disclosure, basal plane dislocations (BPD) of the silicon carbide wafer is less than 200/cm².

[0016] In one embodiment of the present disclosure, basal plane dislocations (BPD) of the silicon carbide wafer is less than 140/cm².

[0017] In one embodiment of the present disclosure, a bar stacking fault (BSF) of the silicon carbide wafer is less than 5/wafer.

[0018] Based on the above, the N-type silicon carbide wafer formed by the method of growing silicon carbide crystals of the embodiments of the present disclosure can have a uniform resistivity distribution. Accordingly, the silicon carbide wafer obtained after the processing steps can have a lower wafer stress, and a wafer geometry can also be improved after processing.

[0025] FIG. 1 is a schematic diagram of a crystal growth device according to an embodiment of the present disclosure. FIG. 2 is a flowchart of a method of growing silicon carbide crystals according to an embodiment of the present disclosure. Hereinafter, a method of growing silicon carbide crystals according to some embodiments of the present disclosure will be described with reference to the crystal growth device shown in FIG. 1 and the flow chart shown in FIG. 2.

[0026] As shown in FIG. 1 and step S10 of FIG. 2, in the crystal growth process, a raw material 110 including a carbon element and a silicon element, and a seed crystal 106 above the raw material 110 are provided into the reactor 102. For example, the raw material 110 is silicon carbide powder, which is placed at a bottom section of the reactor 102 and used as a solid sublimation source. The seed crystal 106 is placed on a top section of the reactor 102. In some embodiments, the seed crystal 106 can be fixed on a seed crystal loading platform (not shown) by an adhesive layer. The material of the seed crystal 106 includes silicon carbide. For example, the seed crystal 106 is 6H silicon carbide or 4H silicon carbide. In other embodiments, the seed crystal 106 includes 6H silicon carbide and 4H silicon carbide.

[0027] As shown in FIG. 1 and step S20 of FIG. 2, in some embodiments, a silicon carbide growth process is performed to form the silicon carbide crystal 108. For example, the growth process further includes performing step S22 and step S24. In step S22, the reactor 102 and the raw material 110 are heated to form silicon carbide crystals 108 on the seed crystals 106. In step S24 of the above growth process, a ratio difference (ΔTz/ΔTx) of an axial temperature gradient (ΔTz) and a radial temperature gradient (ΔTx) of the silicon carbide crystal 108 is adjusted so that the ratio difference is controlled in the range of 0.5 to 3 to form the silicon carbide crystal.

[0028] In the above step S22 and step S24, the silicon carbide crystal 108 is formed on the seed crystal 106 by physical vapor transport (PVT). In some embodiments, the reactor 102 and the raw material 110 are heated by the induction coil 104 to form the silicon carbide crystal 108 on the seed crystal 106. During the manufacturing process, the seed crystal 106 receives the raw material 110 (silicon carbide powder) that is solidified from a gaseous state, and slowly forms semiconductor crystals on the seed crystal 106 until the silicon carbide crystal 108 with the desired size is obtained. Subsequently, referring to FIG. 1 and step S30 of FIG. 2, after the silicon carbide crystal 108 is grown to a desired size, the reactor 102 and the raw material 110 are cooled to obtain a silicon carbide ingot composed of the silicon carbide crystal 108. In some embodiments, the ingots formed may have different crystalline structures depending on the orientation of the monocrystalline crystal seed used. For example, silicon carbide ingots include 4H-silicon carbide, 6H-silicon carbide, and the like. Both 4H-silicon carbide and 6H-silicon carbide belong to the hexagonal crystal system.

[0029] In the above-mentioned embodiment, when the reactor 102 and the raw material 110 are heated to form the silicon carbide crystal 108, the axial temperature gradient (ΔTz) refers to the temperature gradient of the silicon carbide crystal 108 in the thickness direction, while the radial temperature gradient (ΔTx) refers to the temperature gradient of the silicon carbide crystal 108 in a horizontal direction perpendicular to the thickness direction. In some embodiments, the growth rate difference of each crystal direction is utilized to adjust a temperature difference to achieve the ratio difference (ΔTz/ΔTx) in the range of 0.5 to 3. In general, a growth rate of the <11-20> crystal orientation is greater than a growth rate of the <1-100> crystal orientation. In the embodiment of the present disclosure, the growth rates of the two crystal orientations are controlled to be the same, so that the crystals in each axial/radial direction can obtain a certain growth rate for adjusting the ratio difference (ΔTz/ΔTx) to be in the range of 0.5 and 3.

[0030] In some embodiments, the ratio difference (ΔTz/ΔTx) of the axial temperature gradient (ΔTz) and the radial temperature gradient (ΔTx) is controlled in the range of 0.5 to 3 to form the silicon carbide crystal 108. In some embodiments, the ratio difference (ΔTz/ΔTx) of the axial temperature gradient (ΔTz) and the radial temperature gradient (ΔTx) is controlled in the range of 2 to 3 to form the silicon carbide crystal 108. In some embodiments, the ratio difference (ΔTz/ΔTx) of the axial temperature gradient (ΔTz) and the radial temperature gradient (ΔTx) is controlled in the range of 2.5 to 3 to form the silicon carbide crystal 108. In cases where the ratio difference (ΔTz/ΔTx) between the axial temperature gradient (ΔTz) and the radial temperature gradient (ΔTx) are controlled within the above range, the formed silicon carbide crystal 108 can have improved uniformity of the resistivity.

[0031] In some embodiments, when the reactor 102 and the raw material 110 are heated to form the silicon carbide crystal 108, that is, during the growth process of the silicon carbide crystal 108, a doping amount of a nitrogen concentration is further increased so that the nitrogen concentration increases from a first concentration to a second concentration. In some embodiments, the first concentration is 2*10¹⁸ atoms/cm³, and the second concentration is 3*10¹⁸ atoms/cm³. In some embodiments, the first concentration is 2.2*10¹⁸ atoms/cm³, and the second concentration is 2.9*10¹⁸ atoms/cm³. In some embodiments, the first concentration is 2.5*10¹⁸ atoms/cm³, and the second concentration is 2.8*10¹⁸ atoms/cm³. In cases where the doping amount of the nitrogen concentration is controlled within the above range, the uniformity of resistivity of the formed silicon carbide crystal can be further optimized.

[0032] In the above embodiments, the nitrogen concentration can be increased in a linear fashion or in a stepwise fashion. For example, different doping adjustment methods of the nitrogen concentration are described with reference to FIG. 3A to FIG. 3D.

[0033] FIG. 3A to FIG. 3D are charts illustrating different doping adjustment methods for increasing nitrogen concentration in the method for growing silicon carbide crystals according to an embodiment of the present disclosure. As shown in FIG. 3A, in this embodiment, the flow rate of the nitrogen gas is increased linearly as compared with time, thus the nitrogen concentration is also increased in a linear fashion. As shown in FIG. 3B, in this embodiment, the flow rate of the nitrogen gas is increased in a stepwise fashion as compared with time, thus the nitrogen concentration is also increased in a stepwise fashion. As shown in FIG. 3C, in this embodiment, the flow rate of the nitrogen gas is increased stepwise as compared to time. However, in the embodiment of FIG. 3C, the flow rate of the nitrogen gas is increased directly at the start of the process, which is unlike the process shown in FIG. 3B whereby the flow rate of the nitrogen gas is stabilized at 10 sccm for a period of time before the concentration is increased in a stepwise fashion. As shown in FIG. 3D, in this embodiment, the flow rate of the nitrogen gas is increased stepwise as compared to the time. However, in the embodiment of FIG. 3D, the amount of the flow rate of the nitrogen gas increased in each stepwise process is different, and a residence time at specific nitrogen flow rates are also different.

[0034] In the embodiment of the present disclosure, increasing the doping amount of the nitrogen concentration is performed by increasing the flow rate of nitrogen gas in the reactor, so that the increase of the flow of nitrogen is controlled in the range of 10 sccm to 50 sccm, and the method shown in the above FIG. 3A to FIG. 3D can be used to increase the nitrogen concentration in a linear or stepwise fashion. In some embodiments, the increase of the nitrogen flow rate is controlled within the range of 10 sccm to 30 sccm.

[0035] In cases where the above method is used to form silicon carbide crystals, a monocrystalline proportion of the formed silicon carbide crystals and the silicon carbide wafers obtained after processing is 100%, and the resistivity of silicon carbide crystals/wafers is in a range of 15 mΩ·cm to 20 mΩ·cm, preferably within the range of 19 mΩ·cm to 20 mΩ·cm, and a deviation of an uniformity of the resistivity of the silicon carbide wafer is less than 0.4%. In some embodiments, the deviation of the uniformity of the resistivity of the silicon carbide wafer is less than 0.01%. In addition, in some embodiments, basal plane dislocations (BPD) of the silicon carbide crystals/wafers is less than 200/cm². In some embodiments, basal plane dislocations (BPD) of the silicon carbide crystals/wafers is less than 140/cm². In some embodiments, a bar stacking fault (BSF) of the silicon carbide crystals/wafers is less than 5/wafer. Accordingly, a silicon carbide crystal/wafer with a uniform resistivity distribution can be obtained, and a stress of the formed silicon carbide crystal/wafer is also lowered, and the geometry of the wafers after processing is also improved.

[0036] FIG. 4 is a schematic flowchart of a crystal growing method for crystals according to another embodiment of the present disclosure. In some embodiments, the above silicon carbide crystal growth method can be used to perform the crystal growing process. As shown in FIG. 4, in the crystal growing method of the embodiment of the present disclosure, a first crystal seed 202 is provided, wherein the first crystal seed 202 has a first monocrystalline proportion and a first size. In some embodiments, the first monocrystalline proportion is 70% to 80%, and the first size is 200 mm.

[0037] As shown in FIG. 4, a first crystal growth process (N=1) is performed using the first crystal seed 202 to obtain an intermediate crystal 204 with an increased monocrystalline proportion. When it is confirmed that the monocrystalline proportion of the intermediate crystal 204 is not 100%, the intermediate crystal 204 is sliced to obtain the growth crystal seed 204A. Subsequently, the previously obtained growth crystal seed 204A can be used as the crystal seed for the next crystal growing process. For example, in the second crystal growth process (N=2), the growth crystal seed 204A is used to perform the crystal growing process, so as to obtain the intermediate crystal 206 with an increased monocrystalline proportion. When it is confirmed that the monocrystalline proportion of the intermediate crystal 206 is not 100%, the intermediate crystal 206 is sliced to obtain the growth crystal seed 206A. Accordingly, the crystal growing process can be repeated several times (N=X) until the monocrystalline proportion of the intermediate crystal formed by the final crystal seed SD1 is 100%, whereby such intermediate crystal can be designated as the second crystal 250, which completes the crystal growing method in accordance with the embodiments of the present disclosure.

[0038] In the above-mentioned examples, the crystal growth process is performed for the first crystal seed 202 for N times, wherein each of the crystal growth processes will increase the first monocrystalline proportion, and the N times of crystal growth processes are performed until a second crystal 250 having a monocrystalline proportion of 100% is reached. In other words, when an intermediate crystal having a monocrystalline proportion of 100% is confirmed, the above crystal growth process is stopped to form the second crystal 250. In some embodiments, the N times includes more than 3 times of crystal growth processes. In some embodiments, the N times includes more than 3 times and less than 8 times of crystal growth processes. In some embodiments, the N times includes more than 4 times and less than 6 times of crystal growth processes.

[0039] Furthermore, in the above embodiments, each crystal growth process includes adjusting a ratio difference (ΔTz/ΔTx) between an axial temperature gradient (ΔTz) and a radial temperature gradient (ΔTx) of the crystal, so as to control the ratio difference within a range of 0.5 to 3. In the above embodiments, each crystal growth processes includes controlling a doping amount of a nitrogen concentration in a range of 2*10¹⁸ atom/cm³ to 3*10¹⁸ atom/cm³. In some embodiments, each of the crystal growth processes are different. For example, in the embodiments of the present disclosure, the ratio difference (ΔTz/ΔTx) between an axial temperature gradient (ΔTz) and a radial temperature gradient (ΔTx) for each of the crystal growth processes are different, and/or the doping amount of the nitrogen concentration are different, provided that the above ratio difference and the doping amount of the nitrogen concentration are still controlled in the above ranges. By using the above methods, it is possible to grow from a B-grade seed (low monocrystalline proportion) into an A-grade crystal (monocrystalline proportion being 100%) within a certain number of crystal growth processes. As such, it is possible to significantly shorten the time required for forming crystals having a high monocrystalline proportion and a large size.

[0040] FIG. 5 is a schematic flow chart of preparing a first seed crystal used in the crystal growing method according to an embodiment of the present invention. In some embodiments, smaller-sized crystal seeds can also be used in expanding the diameter to form larger-sized crystals. As shown in FIG. 5, in some embodiments, a preliminary crystal seed PX1 is provided, wherein the preliminary crystal seed PX1 has a size A and a monocrystalline proportion of A′. In some embodiments, the size A is smaller than the first size of the first crystal seed 202, and the monocrystalline proportion A′ is larger than the first monocrystalline proportion of the first crystal seed 202. For example, when the first crystal seed 202 has a first monocrystalline proportion of 70% to 80% and a first size of 200 mm, the single crystal ratio A′ of the preliminary crystal seed PX1 is 100%, and the size A of the preliminary crystal seed PX1 is 150 mm.

[0041] As shown in FIG. 5, the preliminary crystal seed PX1 is used for performing a crystal growth process to obtain a first crystal PX2 having the above-mentioned first size and the above-mentioned first monocrystalline proportion. In the embodiment of the present disclosure, the crystal growth process of the preliminary crystal seed PX1 includes adjusting the ratio difference (ΔTz/ΔTx) between the axial temperature gradient (ΔTz) and the radial temperature gradient (ΔTx) of the crystal to control the ratio difference in the range of 0.5 to 3, and to control the doping amount of the nitrogen concentration in the range of 2*10¹⁸ atoms/cm³ to 3*10¹⁸ atoms/cm³. After the first crystal PX2 is obtained, the first crystal PX2 is sliced to obtain the above diameter-expanded first crystal seed 202, and the first crystal seed 202 can be used to perform the steps shown in FIG. 4 to obtain the second crystal 250 having a monocrystalline proportion of 100%. By using the above method, it is possible to grow and expand the diameter of an A-grade seed (monocrystalline proportion being 100%) to form an A-grade crystal (monocrystalline proportion being 100%) with a larger size within a certain number of crystal growth processes. As such, it is possible to significantly shorten the time required for forming crystals having a high monocrystalline proportion and a large size, thus the multiple expansion steps and years of expansion time required for traditional crystal size expansion can be avoided.

[0042] In order to prove that the method of the present invention can produce silicon carbide crystals with uniform resistivity, and can significantly shorten the time required for forming large-sized crystals with a high monocrystalline proportion, the following examples are performed and described.

[0043] In the first example, (i) the ratio difference (ΔTz/ΔTx) between the axial temperature gradient (ΔTz) and the radial temperature gradient (ΔTx), (ii) the doping variation method of the nitrogen concentration, and (iii) the doping amount of the nitrogen concentration of Examples 1 to 7 and Comparative Examples 1 to 4 are adjusted in the manner described in Table 1 and Table 2 below. Furthermore, the growth process is performed in the manner described in FIG. 1 and FIG. 2 to form silicon carbide crystals. The evaluation of the basal plane dislocations, monocrystalline proportion of the wafer, resistivity of the wafer, deviation of an uniformity of the resistivity of the wafer, and bar stacking-fault (BSF) of the obtained silicon carbide wafers are also shown in Table 1 and Table 2.

[0044]

TABLE 1
Item	Example 1	Example 2	Example 3	Example 4	Example 5	Example 6	Example 7
(i) ratio difference	0.5	1	2	0.8	1.7	2.5	3
(ΔTz/ΔTx) between
the axial
temperature
gradient (ΔTz) and
the radial
temperature
gradient (ΔTx)
(ii) doping	From low	From low	From low	From low	From low	From low	From low
variation method of	to high	to high	to high	to high	to high	to high	to high
the nitrogen	(FIG. 3A)	(FIG. 3B)	(FIG. 3C)	(FIG. 3D)	(FIG. 3A)	(FIG. 3A)	(FIG. 3A)
concentration
(iii) doping	Low:	Low:	Low:	Low:	Low:	Low:	Low:
amount of the	greater than	greater than	greater than	greater than	greater than	greater than	greater than
nitrogen	2 × 1018	2.1 × 1018	2.1 × 1018	2.2 × 1018	2.3 × 1018	2.4 × 1018	2.5 × 1018
concentration	High:	High:	High:	High:	High:	High:	High:
(atom/cm3)	less than	less than	less than	less than	less than	less than	less than
	3 × 1018	2.9 × 1018	2.9 × 1018	2.9 × 1018	2.8 × 1018	2.8 × 1018	2.8 × 1018
The obtained silicon carbide wafers:
basal plane	Less	Less	Less	Less	Less	Less	Less
dislocations	than 199	than 195	than 187	than 176	than 164	than 161	than 145
(BPD)(amount/cm2)
Monocrystalline	100%	100%	100%	100%	100%	100%	100%
proportion (%)
Resistivity	15~20	15~20	18~20	18~20	18~20	19-20	19-20
(mΩ · cm)
deviation of an	<0.4%	<0.35%	<0.2%	<0.15%	<0.1%	<0.08%	<0.01%
uniformity of the
resistivity (% dev)
Bar stacking fault	5	3	2	1	2	1	1
(BSF) (ea/wafer)

[0045]

TABLE 2
	Comparative	Comparative	Comparative	Comparative
Item	Example 1	Example 2	Example 3	Example 4
(i) ratio difference	0.4	3	4	0.3
(ΔTz/ΔTx) between
the axial temperature
gradient (ΔTz) and
the radial temperature
gradient (ΔTx)
(ii) doping	Fixed	Fixed	From low	From low
variation method of	concentration	concentration	to high	to high
the nitrogen
concentration
(iii) doping amount	1 × 1018	4 × 1018	Low: greater	Low: greater
of the nitrogen			than 1 × 1018	than 2 × 1018
concentration			High: less	High: less
(atom/cm3)			than 3 × 1018	than 3.5 × 1018
The obtained silicon carbide wafers:
basal plane dislocations	Greater than	Greater than	Greater than	Greater than
(BPD)(amount/cm2)	1000	1500	2500	3000
Monocrystalline	100%	100%	100%	100%
proportion (%)
Resistivity (mΩ · cm)	22~27	22~27	22~27	22~27
deviation of an	>5%	>4%	>2%	>1.5%
uniformity of the
resistivity (% dev)
Bar stacking fault	32	27	16	10
(BSF) (ea/wafer)

[0046] From the experimental results of Examples 1 to 7 shown in Table 1 above, when the ratio difference (ΔTz/ΔTx) between the axial temperature gradient (ΔTz) and the radial temperature gradient (ΔTx) is controlled in the range of 0.5 to 3, and the doping variation method of the nitrogen concentration is adjusted from low concentration to high concentration, and when the doping amount of the nitrogen concentration is controlled in the range of 2*10¹⁸ atoms/cm³ to 3*10¹⁸ atoms/cm³, then the obtained silicon carbide crystal will have a monocrystalline proportion of 100%, and the silicon carbide wafer obtained after processing can have a uniform resistivity distribution (deviation of the uniformity of the resistivity is less than 0.4%), and the basal plane dislocations (BPD) of the wafer can be controlled below 200/cm², the bar stacking fault can be controlled to less than or equal to 5/wafer (ea/wf), and the wafer resistivity (15˜20 mΩ·cm) are also within an ideal range, and preferably in the range of 19 mΩ·cm to 20 mΩ·cm.

[0047] Taking a step further, when the ratio difference (ΔTz/ΔTx) is controlled in the range of 2 to 3, and the doping amount of the nitrogen concentration is controlled in the range of 2.1*10¹⁸ atoms/cm³ to 2.9*10¹⁸ atoms/cm³, then the silicon carbide wafer obtained after processing the silicon carbide crystals has a better uniformity of the resistivity distribution, and less wafer defects and bar stacking faults can be observed. In addition, when the ratio difference (ΔTz/ΔTx) is controlled in the range of 2.5 to 3, and the doping amount of the nitrogen concentration is controlled in the range of 2.4*10¹⁸ atoms/cm³ to 2.8*10¹⁸ atoms/cm³, then the obtained silicon carbide wafer has the best uniformity of the resistivity distribution, and defects such as basal plane dislocations (BPD) and bar stacking faults (BSF) are least observed. Accordingly, the silicon carbide wafer obtained by processing the N-type silicon carbide crystals formed by the method of growing silicon carbide crystals according to the embodiments of the present disclosure can have a uniform resistivity distribution, and the crystal stress is low, and the geometry of the processed wafer will also be improved.

[0048] In comparison, from the experimental results shown in Table 2, referring to Comparative Example 1, when the ratio difference (ΔTz/ΔTx) is not controlled within the range of 0.5 to 3, and the doping method of the nitrogen concentration is not changed, while a fixed doping concentration of 1*10¹⁸ atoms/cm³ is used, the uniformity of the resistivity distribution of the obtained silicon carbide wafer is not good (deviation of the uniformity >5%), and the basal plane dislocation (BPD) results are also not good. Referring to Comparative Example 2, even when the ratio difference (ΔTz/Δx) is controlled within the range of 0.5 to 3, if there is no doping variation in the nitrogen concentration whereby a fixed doping concentration is used, then the uniformity of the resistivity distribution of the obtained silicon carbide wafer is still not good (deviation of the uniformity >4%), and the defects such as basal plane dislocations (BPD) and bar stacking faults (BSF) results are also not good. Referring to Comparative Examples 3-4, although the doping of the nitrogen concentration is varied from a low concentration to a high concentration, if the ratio difference (ΔTz/Δx) is not controlled within the range of 0.5 to 3, and if the doping amount of the nitrogen concentration is not controlled within the range of 2*10¹⁸ atoms/cm³ to 3*10¹⁸ atoms/cm³, although the uniformity of the resistivity distribution is slightly improved compared with Comparative Examples 1-2 (deviation of the uniformity >1.5%), the uniformity of the resistivity distribution is still not within the ideal range, and the defects such as basal plane dislocations (BPD) and bar stacking faults (BSF) results are still not good.

[0049] In the second example, (i) the ratio difference (ΔTz/ΔTx) between the axial temperature gradient (ΔTz) and the radial temperature gradient (ΔTx), (ii) the doping variation method of the nitrogen concentration, and (iii) the doping amount of the nitrogen concentration of the crystal growth process of Examples 8 to 11 and Comparative Examples 5 to 8 are adjusted in the manner described in Tables 3-10 below. In addition, the crystal growth process is performed using the first crystal seed in the manner described in FIG. 4 to form silicon carbide crystals. The evaluation of the basal plane dislocations (BPD), monocrystalline proportion, resistivity, deviation of an uniformity of the resistivity, and bar stacking-fault (BSF) of the obtained silicon carbide crystals in each of the crystal growth processes are also shown in Tables 3-10.

[0050]

TABLE 3
Item	Example 8
Crystal growth process	N = 1	N = 2	N = 3	N = 4	N = 5	N = 6
Monocrystalline	80%	>90%	>95%	>97%	>98%	>99%
proportion of crystal
seed
Size of crystal seed	200 mm	200 mm	200 mm	200 mm	200 mm	200 mm
(diameter)
(i) ratio difference	3	2.8	2.5	2	1.6	0.8
(ΔTz/ΔTx) between
the axial
temperature
gradient (ΔTz) and
the radial
temperature
gradient (ΔTx)
(ii) doping	Fixed	Fixed	From low	From low	From low	From low
variation method of	concentration	concentration	to high	to high	to high	to high
the nitrogen
concentration
(iii) doping	3 × 1018	2.9 × 1018	Low:	Low:	Low:	Low:
amount of the			greater than	greater than	greater than	greater than
concentration			2 × 1018	2.1 × 1018	2.2 × 1018	2.3 × 1018
(atom/cm3)			High:	High:	High:	High:
			less than	less than	less than	less than
			2.8 × 1018	2.7 × 1018	2.6 × 1018	2.6 × 1018
The obtained silicon carbide crystals and wafers
basal plane	Less	Less	Less	Less	Less	Less
dislocations	than 200	than 95	than 186	than 178	than 163	than 141
(BPD)(amount/cm2)
Monocrystalline	>90%	>95%	>97%	>98%	>99%	100%
proportion (%)
Resistivity	15~20	15~20	15~20	18~20	18~20	19~20
(mΩ · cm)
deviation of an	<0.4%	<0.3%	<0.2%	<0.1%	<0.07%	<0.01%
uniformity of the
resistivity (% dev)
Bar stacking fault	5	3	2	2	2	1
(BSF) (ea/wafer)

[0051]

TABLE 4
Item	Example 9
Crystal growth process	N = 1	N = 2	N = 3	N = 4	N = 5	N = 6
Monocrystalline	80%	>90%	>95%	>97%	>98%	>99%
proportion of crystal
seed
Size of crystal seed	200 mm	200 mm	200 mm	200 mm	200 mm	200 mm
(diameter)
(i) ratio difference	2.9	2.5	2	1.8	1.2	0.5
(ΔTz/ΔTx) between
the axial
temperature
gradient (ΔTz) and
the radial
temperature
gradient (ΔTx)
(ii) doping	From high	From high	From high	From high	From high	From high
variation method of	to low	to low	to low	to low	to low	to low
the nitrogen
concentration
(iii) doping	High:	High:	High:	High:	High:	High:
amount of the	less than	less than	less than	less than	less than	less than
nitrogen	3 × 1018	3 × 1018	3 × 1018	2.9 × 1018	2.8 × 1018	2.8 × 1018
concentration	Low:	Low:	Low:	Low:	Low:	Low:
(atom/cm3)	greater than	greater than	greater than	greater than	greater than	greater than
	2.1 × 1018	2.2 × 1018	2.5 × 1018	2.5 × 1018	2.5 × 1018	2.6 × 1018
The obtained silicon carbide crystals and wafers
basal plane	Less	Less	Less	Less	Less	Less
dislocations	than 197	than 182	than 174	than 168	than 155	than 141
(BPD)(amount/cm2)
Monocrystalline	>90%	>95%	>97%	>98%	>99%	100%
proportion (%)
Resistivity	15~20	15~20	18~20	18~20	19~20	19~20
(mΩ · cm)
deviation of an	<0.35%	<0.2%	<0.16%	<0.1%	<0.06%	<0.01%
uniformity of the
resistivity (% dev)
Bar stacking fault	4	3	3	2	1	1
(BSF) (ea/wafer)

[0052]

TABLE 5
Item	Example 10
Crystal growth process	N = 1	N = 2	N = 3	N = 4	N = 5	N = 6
Monocrystalline	80%	>90%	>95%	>97%	>98%	>99%
proportion of crystal
seed
Size of crystal seed	200 mm	200 mm	200 mm	200 mm	200 mm	200 mm
(diameter)
(i) ratio difference	3	2.7	2.2	1.7	1.5	0.6
(ΔTz/ΔTx) between
the axial
temperature
gradient (ΔTz) and
the radial
temperature
gradient (ΔTx)
(ii) doping	Fixed	Fixed	From high	From high	From high	From high
variation method of	concentration	concentration	to low	to low	to low	to low
the nitrogen
concentration
(iii) doping	3 × 1018	2.8 × 1018	High:	High:	High:	High:
amount of the			less than	less than	less than	less than
nitrogen			3 × 1018	2.9 × 1018	2.9 × 1018	2.8 × 1018
concentration			Low:	Low:	Low:	Low:
(atom/cm3)			greater than	greater than	greater than	greater than
			2.2 × 1018	2.2 × 1018	2.5 × 1018	2.5 × 1018
The obtained silicon carbide crystals and wafers:
basal plane	Less	Less	Less	Less	Less	Less
dislocations	than 199	than 185	than 178	than 177	than 164	than 144
(BPD)(amount/cm2)
Monocrystalline	>90%	>95%	>97%	>98%	>99%	100%
proportion (%)
Resistivity	15~20	15~20	18~20	18~20	19~20	19~20
(mΩ · cm)
deviation of an	<0.38%	<0.29%	<0.22%	<0.18%	<0.05%	<0.01%
uniformity of the
resistivity (% dev)
Bar stacking fault	3	2	1	1	1	1
(BSF) (ea/wafer)

[0053]

TABLE 6
Item	Example 11
Crystal growth process	N = 1	N = 2	N = 3	N = 4	N = 5	N = 6
Monocrystalline	80%	>90%	>95%	>97%	>98%	>99%
proportion of crystal
seed
Size of crystal seed	200 mm	200 mm	200 mm	200 mm	200 mm	200 mm
(diameter)
(i) ratio difference	2.8	2.6	2	1.9	1.6	0.7
(ΔTz/ΔTx) between
the axial
temperature
gradient (ΔTz) and
the radial
temperature
gradient (ΔTx)
(ii) doping variation	From low	From low	From low	From low	From low	From low
method of the	to high	to high	to high	to high	to high	to high
nitrogen
concentration
(iii) doping	Low:	Low:	Low:	Low:	Low:	Low:
amount of the	greater than	greater than	greater than	greater than	greater than	greater than
nitrogen	2 × 1018	2.1 × 1018	2.1 × 1018	2.2 × 1018	2.2 × 1018	2.3 × 1018
concentration	High:	High:	High:	High:	High:	High:
(atom/cm3)	less than	less than	less than	less than	less than	less than
	3 × 1018	2.9 × 1018	2.8 × 1018	2.7 × 1018	2.6 × 1018	2.5 × 1018
The obtained silicon carbide crystals and wafers:
basal plane	Less	Less	Less	Less	Less	Less
dislocations	than 198	than 189	than 177	than 162	than 155	than 145
(BPD)(amount/cm2)
Monocrystalline	>90%	>95%	>97%	>98%	>99%	100%
proportion (%)
Resistivity	15~20	15~20	18~20	18~20	19~20	19~20
(mΩ · cm)
deviation of an	<0.28%	<0.21%	<0.16%	<0.12%	<0.09%	<0.01%
uniformity of the
resistivity (% dev)
Bar stacking fault	4	3	2	2	1	1
(BSF) (ea/wafer)

[0054]

TABLE 7
Item	Comparative Example 5
Crystal growth process	N = 1	N = 2	N = 3	N = 4	N = 5	N = 6	N = 7
Monocrystalline	80%	82%	82%	85%	87%	87%	88%
proportion of
crystal seed
Size of crystal	200 mm	200 mm	200 mm	200 mm	200 mm	200 mm	200 mm
seed
(diameter)
(i) ratio	10	9.5	9	8.5	8	7.5	7
difference
(ΔTz/ΔTx)
between the axial
temperature
gradient (ΔTz)
and the radial
temperature
gradient (ΔTx)
(ii) doping	Fixed	Fixed	From low	From low	From low	From low	From low
variation method	concentration	concentration	to high	to high	to high	to high	to high
of the nitrogen
concentration
(iii) doping	8 × 1018	7 × 1018	Low:	Low:	Low:	Low:	Low:
amount of the			greater than	greater than	greater than	greater than	greater than
nitrogen			3.1 × 1018	3.1 × 1018	3.1 × 1018	3.1 × 1018	3.2 × 1018
concentration			High:	High:	High:	High:	High:
(atom/cm3)			less than	less than	less than	less than	less than
			7 × 1018	6.9 × 1018	6.8 × 1018	6.5 × 1018	6.5 × 1018
The obtained silicon carbide crystals and wafers:
basal plane	Greater	Greater	Greater	Greater	Greater	Greater	Greater
dislocations	than 3000	than 2800	than 2600	than 2400	than 2250	than 2000	than 1880
(BPD)(amount/cm2)
Monocrystalline	82(%)	82(%)	85%	87%	87%	88%	88%
proportion (%)
Resistivity	22~27	22~27	22~27	22~27	22~27	22~27	22~27
(mΩ · cm)
deviation of an	>5%	>4.5%	>4.4%	>4.3%	>3.8%	>3.7%	>3.8%
uniformity of the
resistivity
(% dev)
Bar stacking fault	35	32	36	31	38	22	27
(BSF) (ea/wafer)
Item	Comparative Example 5
Crystal growth process	N = 8	N = 9	N = 10	N = 11	N = 12	N = 13
Monocrystalline	88%	89%	90%	90%	91%	92%
proportion of crystal
seed
Size of crystal seed	200 mm	200 mm	200 mm	200 mm	200 mm	200 mm
(diameter)
(i) ratio difference	6.5	5.5	4	3	0.4	0.2
(ΔTz/ΔTx) between
the axial
temperature
gradient (ΔTz) and
the radial
temperature
gradient (ΔTx)
(ii) doping variation	From low	From low	From low	From low	From low	From low
method of the	to high	to high	to high	to high	to high	to high
nitrogen
concentration
(iii) doping	Low:	Low:	Low:	Low:	Low:	Low:
amount of the	greater than	greater than	greater than	greater than	greater than	greater than
nitrogen	3.5 × 1018	3.5 × 1018	3.6 × 1018	3.7 × 1018	3.7 × 1018	3.7 × 1018
concentration	High:	High:	High:	High:	High:	High:
(atom/cm3)	less than	less than	less than	less than	less than	less than
	6.5 × 1018	6 × 1018	6 × 1018	6 × 1018	5.6 × 1018	5.5 × 1018
The obtained silicon carbide crystals and wafers:
basal plane	Greater	Greater	Greater	Greater	Greater	Greater
dislocations	than 1600	than 1430	than 1200	than 1100	than 1100	than 1100
(BPD)(amount/cm2)
Monocrystalline	89%	90%	90%	91%	92%	93%
proportion (%)
Resistivity	22~27	22~27	22~27	22~27	22~27	22~27
(mΩ · cm)
deviation of an	>4.8%	>3.8%	>4.3%	>4.5%	>4.10%	>4%
uniformity of the
resistivity (% dev)
Bar stacking fault	33	27	21	35	18	9
(BSF) (ea/wafer)

[0055]

TABLE 8
Item	Comparative Example 6
Crystal growth process	N = 1	N = 2	N = 3	N = 4	N = 5	N = 6
Monocrystalline	80%	81%	82%	83%	85%	87%
proportion of crystal
seed
Size of crystal seed	200 mm	200 mm	200 mm	200 mm	200 mm	200 mm
(diameter)
(i) ratio difference	9.8	9.6	9	8.3	8	7.2
(ΔTz/ΔTx) between
the axial
temperature
gradient (ΔTz) and
the radial
temperature
gradient (ΔTx)
(ii) doping variation	From high	From high	From high	From high	From high	From high
method of the	to low	to low	to low	to low	to low	to low
nitrogen
concentration
(iii) doping	High:	High:	High:	High:	High:	High:
amount of the	less than	less than	less than	less than	less than	less than
nitrogen	8 × 1018	7.5 × 1018	7 × 1018	6.9 × 1018	6.8 × 1018	6.5 × 1018
concentration	Low:	Low:	Low:	Low:	Low:	Low:
(atom/cm3)	greater than	greater than	greater than	greater than	greater than	greater than
	3.2 × 1018	3.1 × 1018	3.1 × 1018	3.2 × 1018	3.2 × 1018	3.2 × 1018
The obtained silicon carbide crystals and wafers:
basal plane	Greater	Greater	Greater	Greater	Greater	Greater
dislocations	than 3000	than 2800	than 2500	than 2300	than 2250	than 2100
(BPD)(amount/cm2)
Monocrystalline	81%	82%	83%	85%	87%	87%
proportion (%)
Resistivity	22~27	22~27	22~27	22~27	22~27	22~27
(mΩ · cm)
deviation of an	>5%	>5%	>5%	>4.9%	>4.9%	>4.8%
uniformity of the
resistivity (% dev)
Bar stacking fault	38	32	28	22	19	18
(BSF) (ea/wafer)
Item	Comparative Example 6
Crystal growth process	N = 7	N = 8	N = 9	N = 10	N = 11	N = 12
Monocrystalline	87%	88%	89%	90%	90%	90%
proportion of crystal
seed
Size of crystal seed	200 mm	200 mm	200 mm	200 mm	200 mm	200 mm
(diameter)
(i) ratio difference	6.5	5.5	4	3	0.4	0.2
(ΔTz/ΔTx) between
the axial
temperature
gradient (ΔTz) and
the radial
temperature
gradient (ΔTx)
(ii) doping variation	From high	From high	From high	From high	From high	From high
method of the	to low	to low	to low	to low	to low	to low
nitrogen
concentration
(iii) doping	High:	High:	High:	High:	High:	High:
amount of the	less than	less than	less than	less than	less than	less than
nitrogen	6.5 × 1018	6.5 × 1018	6 × 1018	5.8 × 1018	5.8 × 1018	5.7 × 1018
concentration	Low:	Low:	Low:	Low:	Low:	Low:
(atom/cm3)	greater than	greater than	greater than	greater than	greater than	greater than
	3.2 × 1018	3.6 × 1018	3.6 × 1018	3.6 × 1018	3.7 × 1018	3.7 × 1018
The obtained silicon carbide crystals and wafers:
basal plane	Greater	Greater	Greater	Greater	Greater	Greater
dislocations	than 1800	than 1650	than 1400	than 1250	than 1150	than 1100
(BPD)(amount/cm2)
Monocrystalline	88%	89%	90%	90%	90%	91%
proportion (%)
Resistivity	22~27	22~27	22~27	22~27	22~27	22~27
(mΩ · cm)
deviation of an	>4.5%	>4.5%	>4%	>4%	>4.1%	>4.10%
uniformity of the
resistivity (% dev)
Bar stacking fault	22	18	19	20	22	23
(BSF) (ea/wafer)

[0056]

TABLE 9
Item	Comparative Example 7
Crystal growth process	N = 1	N = 2	N = 3	N = 4	N = 5	N = 6
Monocrystalline	80%	82%	82%	83%	85%	86%
proportion of crystal
seed
Size of crystal seed	200 mm	200 mm	200 mm	200 mm	200 mm	200 mm
(diameter)
(i) ratio difference	9.8	9.4	9	8.5	8.3	7.8
(ΔTz/ΔTx) between
the axial
temperature
gradient (ΔTz) and
the radial
temperature
gradient (ΔTx)
(ii) doping variation	Fixed	Fixed	From high	From high	From high	From high
method of the	concentration	concentration	to low	to low	to low	to low
nitrogen
concentration
(iii) doping	7.5 × 1018	7.5 × 1018	High:	High:	High:	High:
amount of the			less than	less than	less than	less than
nitrogen			7.2 × 1018	6.7 × 1018	6.7 × 1018	6.5 × 1018
concentration			Low:	Low:	Low:	Low:
(atom/cm3)			greater than	greater than	greater than	greater than
			3.1 × 1018	3.2 × 1018	3.3 × 1018	3.3 × 1018
The obtained silicon carbide crystals and wafers:
basal plane	Greater	Greater	Greater	Greater	Greater	Greater
dislocations	than 3000	than 2900	than 2650	than 2350	than 2250	than 2100
(BPD)(amount/cm2)
Monocrystalline	82%	82%	83%	85%	86%	87%
proportion (%)
Resistivity	22~27	22~27	22~27	22~27	22~27	22~27
(mΩ · cm)
deviation of an	>4.8%	>4.8%	>4.8%	>4.9%	>4.9%	>4.8%
uniformity of the
resistivity (% dev)
Bar stacking fault	39	37	32	27	25	28
(BSF) (ea/wafer)
Item	Comparative Example 7
Crystal growth process	N = 7	N = 8	N = 9	N = 10	N = 11	N = 12
Monocrystalline	87%	88%	89%	90%	90%	90%
proportion of crystal
seed
Size of crystal seed	200 mm	200 mm	200 mm	200 mm	200 mm	200 mm
(diameter)
(i) ratio difference	6.8	5.5	5	4.8	4	3.2
(ΔTz/ΔTx) between
the axial
temperature
gradient (ΔTz) and
the radial
temperature
gradient (ΔTx)
(ii) doping variation	From high	From high	From high	From high	From high	From high
method of the	to low	to low	to low	to low	to low	to low
nitrogen
concentration
(iii) doping	High:	High:	High:	High:	High:	High:
amount of the	less than	less than	less than	less than	less than	less than
nitrogen	6.5 × 1018	6.5 × 1018	6 × 1018	5.9 × 1018	5.8 × 1018	5.7 × 1018
concentration	Low:	Low:	Low:	Low:	Low:	Low:
(atom/cm3)	greater than	greater than	greater than	greater than	greater than	greater than
	3.4 × 1018	3.6 × 1018	3.6 × 1018	3.6 × 1018	3.7 × 1018	3.9 × 1018
The obtained silicon carbide crystals and wafers:
basal plane	Greater	Greater	Greater	Greater	Greater	Greater
dislocations	than 1800	than 1550	than 1400	than 1250	than 1150	than 1100
(BPD)(amount/cm2)
Monocrystalline	88%	89%	90%	90%	90%	91%
proportion (%)
Resistivity	22~27	22~27	22~27	22~27	22~27	22~27
(mΩ · cm)
deviation of an	>4.5%	>4.5%	>4.3%	>4.3%	>4.0%	>4.0%
uniformity of the
resistivity (% dev)
Bar stacking fault	26	24	19	16	20	16
(BSF) (ea/wafer)

[0057]

TABLE 10
Item	Comparative Example 8
Crystal growth process	N = 1	N = 2	N = 3	N = 4	N = 5	N = 6
Monocrystalline	81%	83%	85%	86%	86%	87%
proportion of crystal
seed
Size of crystal seed	200 mm	200 mm	200 mm	200 mm	200 mm	200 mm
(diameter)
(i) ratio difference	9.3	8	7.8	7	6.8	6.5
(ΔTz/ΔTx) between
the axial
temperature
gradient (ΔTz) and
the radial
temperature
gradient (ΔTx)
(ii) doping variation	From low	From low	From low	From low	From low	From low
method of the	to high	to high	to high	to high	to high	to high
nitrogen
concentration
(iii) doping	Low:	Low:	Low:	Low:	Low:	Low:
amount of the	greater than	greater than	greater than	greater than	greater than	greater than
nitrogen	3 × 1018	3 × 1018	3 × 1018	3 × 1018	3.1 × 1018	3.4 × 1018
concentration	High:	High:	High:	High:	High:	High:
(atom/cm3)	less than	less than	less than	less than	less than	less than
	7 × 1018	6.8 × 1018	6.8 × 1018	6.6 × 1018	6.5 × 1018	6.5 × 1018
The obtained silicon carbide crystals and wafers:
basal plane	Greater	Greater	Greater	Greater	Greater	Greater
dislocations	than 2500	than 2300	than 2250	than 2000	than 1800	than 1500
(BPD)(amount/cm2)
Monocrystalline	82%	84%	85%	86%	86%	89%
proportion (%)
Resistivity	22~27	22~27	22~27	22~27	22~27	22~27
(mΩ · cm)
deviation of an	>5%	>4.5%	>4%	>3.8%	>3.7%	>4.2%
uniformity of the
resistivity (% dev)
Bar stacking fault	39	38	27	23	27	25
(BSF) (ea/wafer)
Item	Comparative Example 8
Crystal growth process	N = 7	N = 8	N = 9	N = 10	N = 11
Monocrystalline	89%	90%	90%	92%	92%
proportion of crystal
seed
Size of crystal seed	200 mm	200 mm	200 mm	200 mm	200 mm
(diameter)
(i) ratio difference	5.8	5	4.4	3.8	3.5
(ΔTz/ΔTx) between
the axial
temperature
gradient (ΔTz) and
the radial
temperature
gradient (ΔTx)
(ii) doping variation	From low	From low	From low	From low	From low
method of the	to high	to high	to high	to high	to high
nitrogen
concentration
(iii) doping	Low:	Low:	Low:	Low:	Low:
amount of the	greater than	greater than	greater than	greater than	greater than
nitrogen	3.4 × 1018	3.5 × 1018	3.6 × 1018	3.7 × 1018	3.71 × 1018
concentration	High:	High:	High:	High:	High:
(atom/cm3)	less than	less than	less than	less than	less than
	6 × 1018	6 × 1018	6 × 1018	5.6 × 1018	5.4 × 1018
The obtained silicon carbide crystals and wafers:
basal plane	Greater	Greater	Greater	Greater	Greater
dislocations	than 1400	than 1250	than 1150	than 1100	than 1050
(BPD)(amount/cm2)
Monocrystalline	90%	90%	91%	92%	93%
proportion (%)
Resistivity	22~27	22~27	22~27	22~27	22~27
(mΩ · cm)
deviation of an	>3.8%	>4.3%	>4.2%	>4.10%	>4.2%
uniformity of the
resistivity (% dev)
Bar stacking fault	25	15	18	14	14
(BSF) (ea/wafer)

[0058] As can be seen from the experimental results of Examples 8-11 shown in Tables 3-6 above, when the ratio difference (ΔTz/ΔTx) is controlled within the range of 0.5 to 3, and the doping amount of the nitrogen concentration is controlled within the range of 2*10¹⁸ atoms/cm³ to 3*10¹⁸ atoms/cm³, then no matter how the doping method of the nitrogen concentration is varied, a B-grade crystal seed (poor monocrystalline proportion) can be grown into an A-grade crystal (monocrystalline proportion of 100%) within 6 times (N=6) of the crystal growth process, and the basal plane dislocations (BPD), the resistivity, the uniformity of the resistivity and bar stacking faults (BSF) can all be controlled within an ideal range, for example, the BSF is less than or equal to 5/wafer.

[0059] In comparison, as can be seen from the experimental results of Comparative Examples shown in Tables 7-10 above, if the ratio difference (ΔTz/ΔTx) between the axial temperature gradient (ΔTz) and the radial temperature gradient (ΔTx) in each crystal growth process is not within the above range, and the doping amount of the nitrogen concentration is outside the above range, then even if the crystal growth process has been carried out for 11 to 13 times, it is still impossible to make the B-grade crystal seed (poor monocrystalline proportion) to grow to form crystals having a monocrystalline proportion of 100%, and the basal plane dislocations (BPD), uniformity of resistivity and bar stacking fault results are still poor. Accordingly, it can be understood that the crystal growth method of the embodiment of the present disclosure can significantly shorten the time required for forming crystals having a high monocrystalline proportion and a large size.

[0060] In the third example, (i) the ratio difference (ΔTz/ΔTx) between the axial temperature gradient (ΔTz) and the radial temperature gradient (ΔTx), (ii) the doping variation method of the nitrogen concentration, and (iii) the doping amount of the nitrogen concentration of the crystal growth process of Example 12 and Comparative Example 9 are adjusted in the manner described in Tables 11˜12 below. In addition, the method as shown in FIG. 5 is performed, whereby a smaller-sized crystal seed is used in a preliminary step (N=0) to expand its diameter to form a larger-sized crystal, and after slicing to form the first crystal seed, the method shown in FIG. 4 is performed by using the first crystal seed to perform the crystal growth process for forming silicon carbide crystals. The evaluation of the basal plane dislocations (BPD), monocrystalline proportion, resistivity, deviation of an uniformity of the resistivity, and bar stacking-fault (BSF) of the obtained silicon carbide crystals in each of the crystal growth processes are also shown in Tables 11˜12.

[0061]

TABLE 11
Item	Comparative Example 12
Crystal growth	(N = 0)	N = 1	N = 2	N = 3	N = 4
process
Monocrystalline	100%	80%	85%	90%	95%
proportion of crystal
seed
Size of crystal seed	150 mm	200 mm	200 mm	200 mm	200 mm
(diameter)
(i) ratio difference	3	2.8	2.5	2	1.2
(ΔTz/ΔTx) between
the axial temperature
gradient (ΔTz) and
the radial temperature
gradient (ΔTx)
(ii) doping variation	From low to	Fixed	Fixed	From low to	From low to
method of the nitrogen	high	concentration	concentration	high	high
concentration
(iii) doping amount	Low: greater	2.8 × 1018	2.7 × 1018	Low: greater	Low: greater
of the nitrogen	than 2 × 1018			than 2.1 × 1018	than 2.2 × 1018
concentration	High: less			High: less	High: less
(atom/cm3)	than 3 × 1018			than 3 × 1018	than 3 × 1018
The obtained silicon carbide crystals and wafers:
basal plane dislocations	Less than	Less than	Less than	Less than	Less than
(BPD)(amount/cm2)	197	186	173	162	144
Monocrystalline	80%	85%	90%	95%	100%
proportion (%)
Resistivity (mΩ · cm)	15~20	15~20	18~20	18~20	19~20
deviation of an	<0.3%	<0.1%	<0.08%	<0.02%	<0.015%
uniformity of the
resistivity (% dev)
Bar stacking fault	200 mm	200 mm	200 mm	200 mm	200 mm
(BSF) (ea/wafer)
basal plane	5	4	4	3	1
dislocations
(BPD)(amount/cm2)

[0062]

TABLE 12
Item	Comparative Example 9
Crystal growth process	N = 0	N = 1	N = 2	N = 3	N = 4	N = 5
Monocrystalline	100%	70%	71%	71%	72%	73%
proportion of crystal
seed
Size of crystal seed	150 mm	200 mm	200 mm	200 mm	200 mm	200 mm
(diameter)
(i) ratio difference	8	7.5	6.8	6	5.8	5.05
(ΔTz/ΔTx) between
the axial
temperature
gradient (ΔTz) and
the radial
temperature
gradient (ΔTx)
(ii) doping variation	From low	Fixed	Fixed	From low	From low	From low
method of the	to high	concentration	concentration	to high	to high	to high
nitrogen
concentration
(iii) doping	Low:	4 × 1018	5 × 1018	Low:	Low:	Low:
amount of the	greater than			greater than	greater than	greater than
nitrogen	3.5 × 1018			5.2 × 1018	5.6 × 1018	5.8 × 1018
concentration	High:			High:	High:	High:
(atom/cm3)	less than			less than	less than	less than
	8 × 1018			8 × 1018	8 × 1018	8 × 1019
The obtained silicon carbide crystals and wafers:
basal plane	Less	Less	Less	Less	Less	Less
dislocations	than 3500	than 3200	than 2800	than 2000	than 1800	than 1500
(BPD)(amount/cm2)
Monocrystalline	70%	71%	71%	72%	73%	74%
proportion (%)
Resistivity	22~27	22~27	22~27	22~27	22~27	22~27
(mΩ · cm)
deviation of an	<5%	<4.9%	<4.5%	<4.2%	<4%	<3.5%
uniformity of the
resistivity (% dev)
Bar stacking fault	200 mm	200 mm	200 mm	200 mm	200 mm	200 mm
(BSF) (ea/wafer)
basal plane	34	30	10	9	7	7
dislocations
(BPD)(amount/cm2)
Item	Comparative Example 9
Crystal growth process	N = 6	N = 7	N = 8	N = 9	N = 10
Monocrystalline	74%	75%	76%	77%	78%
proportion of crystal
seed
Size of crystal seed	200 mm	200 mm	200 mm	200 mm	200 mm
(diameter)
(i) ratio difference	4.46	3.87	3.28	3.2	3.1
(ΔTz/ΔTx) between
the axial
temperature
gradient (ΔTz) and
the radial
temperature
gradient (ΔTx)
(ii) doping variation	From low	From low	From low	From low	From low
method of the	to high	to high	to high	to high	to high
nitrogen
concentration
(iii) doping	Low:	Low:	Low:	Low:	Low:
amount of the	greater than	greater than	greater than	greater than	greater than
nitrogen	6 × 1018	6.2 × 1018	6.5 × 1018	6.5 × 1018	6.6 × 1018
concentration	High:	High:	High:	High:	High:
(atom/cm3)	less than	less than	less than	less than	less than
	8 × 1019	8 × 1020	8 × 1020	7.8 × 1021	7.5 × 1021
The obtained silicon carbide crystals and wafers:
basal plane	Less than	Less	Less	Less	Less
dislocations	1200	than 1100	than 1000	than 900	than 850
(BPD)(amount/cm2)
Monocrystalline	75%	76%	77%	78%	79%
proportion (%)
Resistivity	15~25	15~25	15~25	15~25	15~25
(mΩ · cm)
deviation of an	<3.2%	<3%	<2.8%	<2.8%	<2.5%
uniformity of the
resistivity (% dev)
Bar stacking fault	200 mm	200 mm	200 mm	200 mm	200 mm
(BSF) (ea/wafer)
basal plane	13	14	6	7	6
dislocations
(BPD)(amount/cm2)

[0063] As can be seen from the experimental results of Example 12 shown in Table 11 above, when a smaller-sized A-grade preliminary seed (monocrystalline proportion of 100%) is further used for diameter expansion to form the first crystal seed, and the ratio difference (ΔTz/ΔTx) between the axial temperature gradient (ΔTz) and the radial temperature gradient (ΔTx) of each crystal growth process is controlled within the range of 0.5 to 3, and the doping amount of the nitrogen concentration is controlled within the range of 2*10¹⁸ atoms/cm³ to 3*10¹⁸ atoms/cm³, then no matter how the doping method of the nitrogen concentration is varied, the smaller-sized A grade crystal seed (monocrystalline proportion of 100%) can be grown into a diameter-expanded large size A-grade crystal (monocrystalline proportion of 100%) within 1 time of preliminary diameter expansion and 4 times (N=4) of the crystal growth process, and the basal plane dislocations (BPD), the resistivity, the uniformity of the resistivity and bar stacking faults (BSF) can all be controlled within an ideal range, for example, the BSF is less than or equal to 5/wafer.

[0064] In comparison, as can be seen from the experimental results of Comparative Example 9 shown in Table 12 above, if the ratio difference (ΔTz/ΔTx) between the axial temperature gradient (ΔTz) and the radial temperature gradient (ΔTx) in each crystal growth process is not within the above range, and the doping amount of the nitrogen concentration is outside the above range, then even if one time of preliminary diameter expansion and 10 times of the crystal growth process has been performed, it is still impossible to make the small-sized A-grade crystal seed (monocrystalline proportion of 100%) to grow to form larger size crystals having a monocrystalline proportion of 100%, and the basal plane dislocations (BPD), uniformity of resistivity and bar stacking fault results are still poor. Accordingly, it can be understood that the crystal growth method of the embodiment of the present disclosure can significantly shorten the time required for forming crystals having a high monocrystalline proportion and a large size, thus the multiple expansion steps and years of expansion time required for traditional crystal size expansion can be avoided.

[0065] In summary, the N-type silicon carbide crystals formed by the method of growing silicon carbide crystals of the embodiment of the present disclosure can have a uniform resistivity distribution. Accordingly, the crystal stress of the formed silicon carbide crystals is also lowered, and the geometry of the processed wafer is also improved. In addition, through the crystal growth method of the embodiment of the present disclosure, the time to form a large-sized crystal with a high monocrystalline proportion can be greatly shortened, and crystals having expanded diameter and/or with 100% monocrystalline proportion can be achieved within a certain number of crystal growth processes.

[0066] It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed embodiments without departing from the scope or spirit of the disclosure. In view of the foregoing, it is intended that the disclosure covers modifications and variations provided that they fall within the scope of the following claims and their equivalents.